Vista Missing Registry Error

Hi guys, looking for some urgent help here, hope people can assist.

First off - I phoned Dells technical support to help for this issue, and they couldnt and asked me to ring the software support helpline and gave me a number, I look about it on here and it says I have to pay to use the services? Do I really have to pay? despite the fact I paid an extortionate amount for support and insurance and stuff?

Now - The issue... I had a power cut the other day while shutting down my XPS 420 desktop, when I restarted a few hours later it came up with a boot error, informing me that it couldnt start due to a missing or corrupt registery file and it told me to insert the OS disc and do repair. I do this, go to repair and it comes up with a section where I chose the OS I wish to repair, and there are no options to chose from, yet I am still able to press next, it then comes up with the repair sequence and then quickly after that tells me the repair sequence is complete, and to restart to check whether it has worked. I restart and unfortunately the problem hasnt sorted itself out.

Does anyone know what might be wrong? How I can sort the issue? I'm worried that I'll have to reinstall windows which is something I dont particularly want to do as surely it will mean losing all of my files.

For future reference, if I am forced to reinstall, should I create a partition purely for the OS? Does that then mean that if I have to reinstall windows in the future it means I dont lose my files?